Spider mites moving into dry soybeans

In the driest areas of the Corn Belt, add spider mites to the list of potential yield-robbers in your soybeans.

The hot, dry weather is ideal for 2-spotted spider mites, which holds the potential to inflict some major yield damage to infected fields, says Purdue University Extension entomologist Christian Krupke.

"Mites are found in every field, every year, and usually do nothing of consequence to producers" Krupke says. "However, stressed plants actually provide a more nutritious feast for spider mites than healthy plants do."

Even if you have fields that don't show drought damage as serious as others, don't rule out that the mites could move in, and do so fairly quickly.

"Under conditions where drought-stressed plants are abundant, mites thrive and quickly colonize large areas or fields where stress is more evident," Krupke adds.

It's not always easy to distinguish between spider mite damage and that from other, less dangerous pests. It takes an extra step to effectively scout for spider mites in areas where you see yellowing soybean plants. And, be thorough.

"To confirm the presence of mites, shake some discolored soybean leaves over a white piece of paper. Watch for small, dark specks moving about on the paper. Also, look for very tiny, fine webbing on the undersides of the discolored leaves," Krupke says. "Once spider mites have been positively identified in the damaged areas of the field, it is essential that portions of the entire field be scouted to determine the limits and range of infestation."

If you confirm an infestation, be ready to act quickly. Spider mites can be tough to kill, Krupke says, and if you don't treat sufficiently, they can quickly come back and be on the move again.

"Surviving spider mites are able to repopulate a field much more quickly than their natural predators, which are usually also wiped out by these chemical applications," he says.

But, Mother Nature holds the best defense from spider mites. "Significant rain doesn't control spider mites but helps the soybean plant become more vigorous and healthy. This, in turn, makes the 'juices' of the plant less nutritious to the mites, and makes mites less likely to reproduce as quickly," Krupke says. "We can't make it rain, but we can take steps to make sure that mite scouting and treatment is prioritized until conditions improve. Mites don't need to reach outbreak levels, but vigilance is important in early stages of infestation."